Acrylic prepolymer and process for encapsulation of photocells

Abstract

Acrylic prepolymer comprising: from 10 to 50% by weight of units derived from at least one alkyl acrylate, the alkyl group having from 4 to 12 carbon atoms, from 30 to 60% by weight of units derived from at least one alkyl methacrylate, the alkyl group having from 1 to 5 carbon atoms, and from 10 to 40% by weight of units derived from methyl acrylate. The prepolymer is used to encapsulate photocells, connected to one another by conducting wires and positioned on a support plate, by casting a resin into the space located between the support plate and a second protective plate, the resin being obtained by mixing 100 parts of the acrylic prepolymer, from 0.1 to 4 parts of a vanadium arenesulphonate and from 0.5 to 4 parts of a free-radical initiator, at a temperature between 10° and 70° C. and for a sufficient time to solidify the polymeric resin at the temperature selected.

What is claimed is: 
     
       1. An acrylic prepolymer comprising: from 10 to 50% by weight of units derived from at least one alkyl acrylate, the alkyl group having from 4 to 12 carbon atoms,   from 30 to 60% by weight of units derived from at least one alkyl methacrylate, the alkyl group having from 1 to 5 carbon atoms, and   from 10 to 40% by weight of units derived from methyl acrylate.   
     
     
       2. A prepolymer according to claim 1, possessing a density at 20° C. between 0.960 and 0.975. 
     
     
       3. A prepolymer according to claim 1 or 2, possessing a refractive index between 1.43 and 1.44. 
     
     
       4. A prepolymer according to claim 1, further comprising from 20 to 200 ppm of a polymerization inhibitor. 
     
     
       5. A prepolymer according to claim 1 or 4, further comprising units derived from a fourth comonomer selected from the group consisting of acrylic acid, methyacrylic acid, and ethylene glycol monomethacrylate. 
     
     
       6. A process for the manufacture of the acrylic prepolymer according to claim 1, comprising copolymerizing (a) from 10 to 50% by weight of at least one alkyl acrylate, the alkyl group having from 4 to 12 carbon atoms, (b) from 30 to 60% by weight of at least one alkyl methacrylate, the alkyl group having from 1 to 5 carbon atoms, and (c) from 10 to 40% by weight of methyl acrylate in the presence of a free-radical initiator and a chain transfer agent, at a temperature between 60° and 85° C., until a viscosity of between 1.5 and 10 poises is obtained.